The reaction involving the combination of two moles of isobutane has been previously reported, for example, in the Journal of Organic Chemistry, 6, 647 (1941) and 29 (6), 1497 (1964). This abnormal reaction of isobutane with certain olefins has become known as self-alkylation or hydrogen transfer. The overall reaction involving isobutane and C.sub.5 or higher olefins results in the production of a branched octane and a paraffin corresponding in carbon content to the olefin employed as follows: EQU 2 i-C.sub.4 H.sub.10 + C.sub.n H.sub.2n .fwdarw.i-C.sub.8 H.sub.18 + C.sub.n H.sub.2n+2
The self-alkylation referred to above is distinguishable from direct alkylation of an isoparaffin, and in the typical instance, with a normal C.sub.2 to C.sub.4 olefin. In direct alkylation the number of carbons in the product correspond to the sum of the carbons of the isoparaffin and olefin reactants. For example, the direct alkylation of isobutane and ethylene forms a C.sub.6 isomer, such as 2,3-dimethylbutane, as follows: EQU i-C.sub.4 H.sub.10 + C.sub.2 H.sub.4 .fwdarw.i-C.sub.6 H.sub.14
with respect to the self-alkylation reaction, the ionic reaction involving hydrogen transfer has been conducted in the presence of an acid catalyst, typically concentrated (95+ weight percent) sulfuric acid. While sulfuric acid is extremely effective as a catalyst in self-alkylation reactions, the acid presents substantial problems from the standpoint of safety and the cost of equipment in view of the highly corrosive nature of this material. In addition to the disadvantages associated with the use of an acid catalyst in the process, there exists problems in the disposal of such waste products as sulfuric acid sludge. Further, the use of a liquid acid catalyst requires that the same be recovered from the reaction by air burning and reconstitution which additionally presents problems of safety along with meeting environmental requirements necessitating the use of costly equipment.
It is therefore an object of this invention to provide a process for the self-alkylation of isobutane which can be undertaken in the presence of a solid catalyst.
Another object of this invention is to provide a process for the self-alkylation of isobutane which avoids the use of highly corrosive materials.
Yet another object of this invention is to provide a process for the self-alkylation of isobutane which does not entail disposal of corrosive waste products.
A further object of this invention is to provide a combined isomerization and self-alkylation process wherein n-butane is converted to high octane components.
Other objects and advantages will become apparent from a reading of the following detailed description and examples.